1. Field of the Invention
The present invention relates to a method of controlling an automatic transmission for a vehicle. More particularly, the method relates to a method of calculating whether the rear wheels of the vehicle are slipping during a cornering maneuver, and prohibiting downshifting of the automatic transmission in a case where the rear wheels have been determined to be slipping.
2. Description of the Background Art
Generally speaking, an automatic transmission automatically changes its gear ratio in accordance with an operating state of a vehicle. As a throttle is opened, by depressing an accelerator pedal quickly or past a certain critical point, the automatic transmission downshifts in order to increase the gear ratio, and to rapidly accelerate the vehicle (downshift control or kick-down).
One example of a method of controlling a gear change ratio to a lower limit during cornering is disclosed in Japanese Patent Laid-Open Publication Hei 8-210456.
With an vehicle, an accelerator is often depressed during cornering, in order to enable rear wheels to slide and to expedite cornering, which means that an automatic transmission is downshifted.
When the accelerator is pressed down extensively while the rear wheels are slipping, the automatic transmission undergoes a large gear ratio change, which will lead to an abrupt change in slip ratio of the rear wheels while the vehicle is cornering, adversely affecting ride quality.